Time-dependent manipulation of ultracold ion bunches

Abstract

The combination of an ultracold ion source based on photoionization of a laser-cooled gas and time-dependent acceleration fields enables precise manipulation of ion beams. We demonstrate reduction in the longitudinal energy spread and transverse ͑de͒focusing of the beam by applying time-dependent acceleration voltages. In addition, we show how time-dependent acceleration fields can be used to control both the sign and strength of the spherical aberrations. The experimental results are in close agreement with detailed charged particle tracking simulations and can be explained in terms of a simple analytical model.

Optimization of the current extracted from an ultracold ion source

“…A higher saturation parameter of the excitation laser beam means a higher excited state fraction and therefore a higher initial peak current. Hence, the expected behavior of the peak current is to be proportional to the excited state fraction: I peak ∝ f (s, δ → 0), from equation (15). This relation is also plotted in the figure as a solid line.…”

“…In addition, new ways to adjust the longitudinal and transverse properties of the extracted ion beams by employing pulsed acceleration fields have been demonstrated [12,14,15]. However, the reduced brightness achieved so far with MOTIS/UCIS (≈ 10 4 A m −2 sr −1 eV −1 , demonstrated for a chromium MOTIS [11]) is two orders of magnitude lower than the established brightness of a gallium LMIS [2], limiting the application of the source in FIBs.…”

“…Achieving a low energy spread then requires a low extraction field, which unfortunately leads to a reduction of the beam brightness due to Coulombic interactions [7,13]. If, on the other hand, only a small volume of the entire cloud of atoms is selected by crossing the excitation laser beam with the ionization laser beam at the center of the atomic cloud [7,12,14,15], a proportionally lower energy spread at the same extraction field can be achieved. However, because the ionization volume is smaller, less current is extracted and, in addition, pulsed operation of the source is required.…”

Bright focused ion beam sources based on laser-cooled atoms

“…Particle tracking simulations with Coulombic interactions are depicted as solid curves; simulations without Coulombic interactions as dashed curves (from Ref. 153). …”

Patterned Rydberg excitation and ionization with a spatial light modulator

“…In the case of Rydberg atoms the acceleration fields will strip the Rydberg atoms of their valence electron, and the imaging procedure is the same as for ions. Chromatic and spherical abberations of the accelerator are sufficiently small that, during the time of flight, the ion pattern does not deform, apart from a global magnification of a factor 46 [42]. The detector, consisting of a double micro-channel plate and phosphor screen, is able to spatially resolve single ions and thus provides a direct measurement of the ion or Rydberg distribution as it was in the MOT, projected onto a plane.…”